Patent GB-1058981-A (GB)
Title: Acoustically supported motion sensor
Inventor: ENSLEY DONALD LUTHER
IPC: G01P15/13
Filed: 1964-02-12
Abstract: 1,058,981. Bearings. HARVEST QUEEN MILL & ELEVATOR CO. Feb. 12, 1964, No. 5880/64. Heading F2A. [Also in Division G1] Motion sensing apparatus comprises means for suspending a body in a compressible medium by the time average of a vibratory field of force, such as an acoustic field, and means responsive to movement of the body. Visually read accelerometer.-A cylindrical piezo-electric transducer 214, Fig. 1A, fed from an oscillator 230 produces a radially divergent standing wave sound field, in the container 211. The field restrains a cylindrical mass 220 at a reference position, deviations from which produce restoring forces on the mass. Such deviations may be caused by accelerations of the container 211 and may be detected by the reflection of light from a lamp 221 on to scales 225, 226 calibrated in accelerations. The mass 220 may be so shaped, Fig. 1G (not shown), that the field exerts a circumferential force thereon, causing it to rotate, thus increasing its inertia. Accelerometer with capacitative read-out.- An inertial mass M, Fig. 1D, comprising cylindrical portions 264, 265, and a spherical portion 262 is maintained coaxial with a cylindrical container 250 by piezo-electric transducers 254, 256, which produce a strong restoring force on cylinders 264, 265 if they tend to deviate from a datum position. A spherical piezo-electric transducer 262 produces a weaker ultrasonic field which restrains the mass M axially but allows axial deviations to occur when container 250 is accelerated axially. These deviations vary capacitances formed by plates 270, 271, and 272, 273 which in turn vary the capacitance between electrodes 300, 301 in an inert gas subject to non-linear ionization to which an R.F. field is applied from an oscillator 293. For small capacitance changes a proportional D.C. voltage is produced between electrodes 300 and 301 and this is amplified and applied to a cathode-ray-tube 313, meter 314 and recorder 315 to indicate accelerations. Photo-electric turn indicators and accelerometers.-A turn indicator, Fig. 1E, comprises a piezo-electric transducer 214 which sets up a radially divergent ultrasonic field which restrains a transparent cylindrical mass 220 coaxial with the container 211. A lamp 322. and lens 323 produce beams of parallel light. which are plane polarized. by polarizers 324, 325. The transparent mass 220 has the effect of rotating the plane of polarization of the light through an angle dependent upon its angular position relative to the container 211. The cells 328 and 329 are connected by choppers to an input transformer 331 the output of which is amplified and used to. drive the container 211 back to its starting position by means of a Selsyn system 342, 343. In a modification, Fig. 10 (not shown), the mass 220 has metallic foil on its inner and outer surfaces and a coil wound inside it the ends of the coil being connected to the foils. The coil is in the field of a coil energizing the piezo-electric transducer and the voltage derived therefrom acts to stabilize the mass 220. In a further modification, Fig. 1F, the mass M comprises cylindrical portions 264, 265 and is restrained by acoustic fields produced by two cylindrical piezo-electric transducers and a spherical transducer 262. A servo system similar to that shown in Fig. 1E may be provided. In Fig. 2, the transparent body is in the form of a cylinder G and is supported by six piezo-electric transducers Q1 ... Q6, the feeds to which are so phased that the body oscillates rapidly about its mean position shown. Magnets M, M<SP>1</SP> co-operate with windings N, N<SP>1</SP> to bring the body G to the position where the ultrasonic suspension operates. The apparatus may also measure acceleration by providing the body G with an opaque coating so that its position perpendicular to its axis is determined by the amount of light it allows to pass between a further light source and detector. In a modification, Fig. 7 (not shown), the body G is replaced by a number of smaller bodies which are restrained by an axial ultrasonic generator.